Clutches

ABSTRACT

A reproduction machine having a document scanning system has an improved recycling clutch for operating the system. The clutch has a rotatable input plate and a rotatable output plate. A pawl pivotally mounted on the input plate is biased into engagement with a notch on the output plate. A rotatable timing pulley driven by the input plate periodically contacts the pawl to disengage the latter from the output plate to effect release of the clutch at intervals greater than a revolution of the input plate. An arcuate ramp maintains the disengagement of the pawl from the output plate for a sufficient length of time to permit rotation of the latter in the reverse direction greater than one revolution via a biasing spring.

[451 Sept. 16, 1975 .1 CLUTCHES [75] Inventor: John Hayward Cook,

Sawbridgeworth, England [73] Assignee: Xerox Corporation, Stamford,

Conn.

[22] Filed: June 11, 1974 [211 App]. No.: 478,210

[30] Foreign Application Priority Data Dec. 21, 1973 United Kingdom59532/73 [56] References Cited UNITED STATES PATENTS l/19l8 Cater 74/824/1950 Laxo 192/29 10/1958 Eastman 192/28 X Johnson 192/28 X Larsson74/82 Primary ExaminerAllan D. Herrmann [57] ABSTRACT A reproductionmachine having a document scanning system has an improved recyclingclutch for operating the system. The clutch has a rotatable input plateand a rotatable output plate. A pawl pivotally mounted on the inputplate is biased into engagement with a notch on the output plate. Arotatable timing pulley driven by the input plate periodically contactsthe pawl to disengage the latter from the output plate to effect releaseof the clutch at intervals greater than a revolution of the input plate.An arcuate ramp maintains the disengagement of the pawl from the outputplate for a sufficient length of time to permit rotation of the latterin the reverse direction greater than one revolution via a biasingspring.

5 Claims, 4 Drawing Figures CLUTCHES BACKGROUND OF THE INVENTION Thisinvention relates to clutches, particularly for use in controlling themovement of a carriage, and to drive systems incorporating suchclutches.

Drive systems are known in which, during operation, a driven elementenergizes a biasing means as it is driven in one direction from a restposition, and a clutch automatically disengages the drive after apredetermined movement of the driven element whereby the latter isreturned to its rest position under the influence of the biasing means.The present invention is particularly concerned with clutches suirablefor performing such automatic disengagement of the drive which arehereinafter and in the claims referred to as recycling clutches.

One application of such a clutch is to be found in a photocopyingmachine such as an electrostatographic reproduction machine as describedin British Patent Specification No. 995,413 which includes lamps forexposing successive portions of the document to be copied to aphotosensitive surface. These lamps which are carried on a carriage arescanned slowly across the document and are then quickly returned totheir initial (start-of-scan) positions, at the end of the scanningstroke. Normally the carriage is driven in one direction which acarriage carries one or more mirrors by which images of the successiveportions of the document to be copied are directed onto a photosensitivesurface. Normally the light is directed onto the photosensitive surfacethrough a fixed aperture and the photosensitive surface is arranged tomove past the aperture during exposure of the document. With such anarrangement it is essential that the movement of the carriage besynchronized with the movement of the photosensitive surface which isusually in the form of a drum.

Conveniently such a carriage is driven by means of a cable passingaround a capstan mounted on a drive shaft and one suitable clutchcomprises rotatable input and output elements of which the outputelement carries a pawl which is normally engaged by a dog on the inputelement. The input element is continuously driven, the pawl beingreleased by engaging a fixed stop member once during each revolution ofthe clutch whereby the carriage may be returned to its start-ofscanposition under the influence of a spring, the output element of theclutch rotating in the reverse direction for slightly less than onerevolution when it is again picked up by the dog on the still rotatinginput element. With such an arrangement, in order to ensure that themovement of the carriage is synchronized with that of the photoreceptor,the capstan must be of the same size as the photoreceptor drum, androtate at the same speed as the drum. This is generally convenient wherethe capstan can be mounted on the axis of the photoreceptor butparticularly where it is desired to arrange the capstan in a differentlocation, space requirements may make a capstan of these proportionsinconvenient. If the capstan is to be of reduced size yet drive thecarriage synchronously with the photoreceptor it must rotate faster thanthe photoreceptor and through more than a single revolution for eachscanning movement of the carriage. One way of achieving this isdescribed in our co-pending US. Application Ser. No. 367,996, filed June7, 1973, in which the drive to an optics carriage drive shaft of anelectrostatographic reproduction machine is transmitted via a timingpulley rotatably mounted on a driven shaft arranged parallel to the0ptics drive shaft. (The capstan is fixed on the optics drive shaft.) Acable drive connects this pulley with a pulley on the optics driveshaft. Secured on the driven shaft is a pawl plate and a pawl ispivotally mounted on the timing pulley about an axis disposed radiallybeyond the periphery of the pawl plate. The pawl normally engages anotch in the pawl plate to complete the drive to the optics drive shaft.A fixed (but adjustable) pawl knock-out plate disengages the pawl fromthe notch in the pawl plate once in each driving revolution of thepulley so permitting the optics drive shaft to rotate in reversedirection under the influence of a spring connected to the capstan toreturn the carriage to the startof-scan position. More than onerevolution of the optics drive shaft is achieved by making the diameterof the timing pulley a whole number of multiple of the diameter of thepulley on the optics drive shaft.

In the system described in our aforesaid co-pending US. Application Ser.No. 367,996, the timing element carries the pawl and forms part of theclutch assembly. The pawl plate rotates once for each scanning movementof the carriage. This means that it is sufficient merely to knock thepawl out of the notch in the plate and allow it to ride around theperiphery of the pawl plate until it drops back into the notch, afterslightly less than one revolution of the timing pulley (since the pawlplate is still rotating). Stated another way, the output element of theclutch rotates (in one direction) through slightly less than onerevolution during scanning and also in (reverse direction) duringrescan. However, removing the timing element from the direct drive tothe carriage drive shaft requires that like the capstan the outputelement of the clutch shall rotate through greater than a revolutionduring scanning and rescan. It is not sufficient in this circumstancemerely to effect release of the clutch since then it would becomere-engaged before rescan had been completed.

BRIEF SUMMARY OF THE INVENTION It is an object of the present inventionto provide a recycling clutch which has the above described advantagesand at the same time permits the drive to be transmitted directly to theoptics drive shaft without the timing element (pulley) being directlyloaded. The present invention also provides means for maintaining theclutch disengaged during a sufficient operational interval of time topermit the required rotation.

To this end, the invention consists in a recycling clutch comprisingrotatable input and output elements,

direction under the influence of a biasing means through greater thanone revolution.

In the clutch of the present invention, the pivotally mounted driveengagement means suitably takes the form of a pawl mounted on the inputelement and biased drivingly to engage a stop or surface on the outputelement. Preferably the clutch is maintained disengaged for the requiredoperational interval of time by the pawl engaging a ramp or cam surface.

The timing element may include a pulley driven from a pulley fixedagainst rotation with respect to the input element and including stopmeans adapted to engage the pawl once in each N revolutions where theratio of the diameters of the pulleys is N: 1. Or the pulleys may bereplaced by meshing gears.

From another aspect, the invention consists in a carriage drive assemblyincorporating a recycling clutch as described above.

And from a further aspect, the invention consists in a photocopyingmachine having a document scanning system incorporating such a recyclingclutch.

In order that the invention may be more readily understood. referencewill now be made to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows schematically anembodiment of carriage drive assembly of a document scanning system ofan electrostatographic reproduction machine in accordance with thepresent invention.

FIG. 2 illustrates the optical arrangement of the scanning system shownin FIG. 1.

FIG. 3 is a section through an embodiment of clutch according to thisinvention.

FIG. 4 is a section along the line AA of FIG. 3.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1 there is showna carriage drive assembly according to the invention applied to thedocument scanning system of an electrostatographic machine.

In the practice of electrostatography, various procedures may befollowed. By way of illustration an electrostatographic image may beformed on a surface comprising a layer of photoconductive insulatingmaterial affixed to a conductive backing which is electrically chargeduniformly to render it photosensitive, is then exposed to light from agiven image so that an electrostatic latent image is formed thereon inaccordance with the light image cast thereon, and finally is caused tobe approached by a developer material, which may be fine coloredparticles carrying electric charge (referred to as toner), or it may bein liquid form, so that the developer material is attracted selectivelyto the electrostatic latent image, converting the latent image into avisible image. The powder or liquid may subsequently be transferred to asheet of paper and suitably affixed to it so as to form a permanentprint.

One method of exposing the photoconductive layer to light from a givenimage comprises scanning a lamp or lamps across a document to be copied,the image being projected onto the photoconduetive surface by means of asuitable optical system. One system for achieving this is described inBritish Patent Specification 995,413 where lamps which expose successiveportions of a document to the photosensitive surface as they are scannedslowly across the document, are

mounted on a carriage. At the end of the scanning stroke, the lamps arequickly returned to their start position.

The optical arrangement of the system shown in FIG. 1 is illustratedschematically in FIG. 2 and for clarity will be described first, itbeing noted that the views in FIGS. 1 and 2 are taken from the same sideof the system. A platen 10 is provided to support a document 1 l whichis to be copied. A scanning mirror system includes two movable mirrors12 and 13 shown in their extreme left and right hand positions (in FIG.2) in full and dotted outline respectively. The mirror 13 is arranged tomove at half the speed of the mirror 12 during scanning to maintain theoptical distance constant between the document 11 and a lens 14. Atubular lamp 15 extending across the palten 10 parallel to the mirror 12and in fixed relation to the latter moves with the mirror 12. The lamp15 serves to illuminate the document through the platen 10 duringscanning. An optical path extending from the platen 10 to the lens 14continues beyond the lens to be reflected in sequence by mirrors 16 and17 towards a photoreceptor drum 18. The photoreceptor may take otherforms than a drum, e.g., it may be in the form of a belt or aphotoconductive copy sheet.

Referring now to FIG. 1, the mirrors 12 and 13 are mounted respectivelyon carriages 21 and 22 which run on guide rods. tubes or the like 23 and24 respectively. A common guide bar 25 is provided at the opposite sidesof the carriages to support and stabilize the carriages. The carriage 21also carries the lamp 115.

In FIGv 1 the carriages 21 and 22 are shown in their start-of-scan"positions and during scanning they move from left to right.

The carriage 21 is driven by a cable 26 via a capstan 27 fixedly mountedon a shaft 28 which is driven from the main shaft of the machine througha belt 29 via a clutch ofthis invention schematically illustrated inFIG. 1 by the input element 41 thereof which is mounted on shaft 28 forrotation with respect thereto. The belt 29 which also drives thephotoreceptor drum passes over a pulley 29a fixed to the clutch inputelement 41 for rotation therewith. The movement of the carriage 21 iscontrolled by a single pulley and cable arrangement 30, 30 wherein thecable 30 extends between the carriage 21 and a fixed point on themachine frame over the pulley 30' which is mounted on the carriage 22.The cable 30 is held in tension by means of a secondary cable drive 31from a smaller diameter capstan 31:! attached to the capstan 27. Asshown the cable SI is connected at its end opposite the capstan, to thecarriage 22 and a tension spring 33 is interposed in the cable fortensioning. The drive capstan 27 is operatively connected to the beltdrive 29 during scanning by means of a clutch according to thisinvention which will be described below. During scanning a spring 34connected between the capstan and a fixed point is loaded and providesthe energy for returning the carriages to their start-of-scan positionswhen the clutch is disengaged. For convenience the return of thecarriages to their start-of-scan positions is termed re-scan".

In its start-of-scan position, the carriage 21 rests against an end stopor buffer 35 and at the end of the rescan stroke the carriage collideswith this stop. In order to soften the collision and avoid damage to thesystem, particularly the lamps, which are delicate. especially when hot,the velocity of the carriage 21 when it reaches the end stop iscontrolled by a suitable dashpot arrangement 36. r

The embodiment of clutch schematically. represented in FIG. 1 is alsoillustrated in FIGSQ3 and 4 and will now be described in detail. Theclutch comprises an input element defined by a plate 41 mounted'on theshaft 28 for rotation relative thereto and an output element defined bya pawl plate 42 having a single notch 43 and which, like the capstan 27,is mounted on the the clutch is engaged andyreferring to FIG. 1, the capstan 28 is rotated to drive the carriages 21 and 22 in the scanningdirection, the scanning movement of the carriages being synchronizedwith the rotation of the photoreceptor through the timing belt 29 whichdrives, via the clutch, the shaft 28. In the drive arrangementillustrated, the capstan 27 is of lesser diameter than the photoreceptordrum and has to rotate through greater than one revolution in order toeffect the required scanning movement of the carriages, before theclutch is disengaged. This is achieved, in accordance with theinvention, in the following manner.

A pulley 46 secured to or integral with the plate 41 or as shown thepulley 29a and rotatable about the shaft 28 on the same bearing as plate41 and pulley 29a drives a timing pulley 47 through a belt 48; thepulley 47 is mounted for rotation on a shaft 49 supported from themachine frame M, specifically a side plate thereof being shown. Thepulley 47 carries by means of a spacer 47a a knock-out member 50,located in the same plane as pawl 45 and having a pin 51 extendingbetween its pear-shaped side walls adjacent the extremities thereof. Thepin 51 is arranged to engage the tail 45a of pawl 45, and effect releaseof the clutch once in each N revolutions of the shaft 28, where thediameter oftiming pulley 47 is N times that of pulley 46. In theembodiment illustrates N 2. Upon release of the clutch, the capstan 27is rotated in reverse direction by the spring 34 to effect high speedrescan of the carriages 21 and 22.

It will be understood that during rescan, the capstan has to rotate inreverse direction through greater than one revolution where N 2, throughgreater than two revolutions where N 3, etc., and in order to permitthis means must be provided to maintain the clutch disengaged for asufficient length of time to avoid reengagement of pawl 45 and notch 43before rescan has been completed. This is achieved in the embodimentillustrated by a boss 52 on pawl 45 running on the outside surface of afixed arcuate ramp 53 secured to the side plate 48 followingdisengagement so as to maintain the pawl 45 disengaged for a sufficientlength of time to permit rescan to be completed.

The operation of the clutch during one copy cycle of the machine willnow be described. At the start of the cycle the clutch is engaged andthe carriages 21 and 22 are in their start-of-scan positions. The beltdrive 28 is started so as to rotate the photoreceptor drum and,

through the clutch, the capstan 27 to drive the carriages in thescanning direction. Each scanning cycle (which includes rescan)corresponds to N revolutions of the shaft 28 and accordingly the scanstroke of the carriages must be effected in less than N revolutions.

Suitably, the carriages reach the ends of their scanning strokes,during'which they move in synchronism with the photoreceptor, after Nrevolutions of the capstan 27 (and shaft 28), whereupon the clutch isdisengaged by the pin 51 engaging the pawl and disengaging the latterfrom the notch 43 in the pawl plate 42 to effect release of the clutch.During scanning the spring 34 is wound up by reason of its connectionbetween capstan 27 and a fixed point. The capstan now rotates in reversedirection under the influence of the spring 34 through N V2 revolutionsto rescan the carriages, the pawl being held disengaged for sufficienttime to permit this by ramp 53. The time interval required is that fortheeam to rotate through N l revolutions'after which the pawl 45 cannotreengage the notch 43 in pawl plate 42 before rescan is completed. Thelength of ramp 53 is dependent on the choice of the spring 34 and otherfactors determining the rescan speed of the carriages (e.g., the effectof the dashpot 36), and may, for example be approximately semicircular.As the boss 52 runs off the end of ramp 53, the pawl 45 is returned toits drive engaging position, e.g., by a spring 54 connected between thepawl 45 and plate 41, and picks up pawl plate 42 at the start of thenext scanning stroke. Thus, the scanning cycle of N revolutions of shaft28 comprises a scanning stroke of N V2 revolutions and rescan during theremaining half revolution.

While a particular embodiment of the invention has been described, itwill be appreciated that various modifications may be made to thespecific details referred to herein without departing from the scope ofthe invention as defined in the appended claims. For example, the valueof N may be different from the values described, depending on the sizeof the capstan and the length of the carriage scanning stroke.

Furthermore although a scanning drive for the carriages is describedwhich is effective through a capstan, it will be understood that otherdrive systems are envisaged within the scope of this invention. Also,while document scanning systems described above include two carriages, adifferent number of carriages, including a single carriage, may beprovided.

Following the making of a desired number of copies anelectrostatographic apparatus as described above may enter a shutdowncycle during which the drive to the photoreceptor, and thus therecycling clutch, is maintained so as for example to complete thedelivery of the last copy sheet to the output tray and to completecleaning of residual developer material from the drum. With theconstruction described above, the clutch will re-engage and drive thecarriages 2'1, 22 in the scanning direction during this shutdown cycle.In order to prevent re-engagement of the clutch during this shutdowncycle, in a modification, the ramp 53 may be movably mounted andsuitable means provided for moving the arcuate ramp 53 along the circleof which it forms an arcuate position in the anticlockwise direction inFIG. 3 during rescan following the scan corresponding to the last copyand after the boss 52 has engaged the ramp 53. By so moving the ramp 53(while the boss 52 is running thereon) by a suitable amount,

re-engagement of the clutch can be prevented during the shutdown cycle.

What is claimed is:

l. A reproduction machine having a document scanning system, and animproved means for operating the latter, said means comprising:

a recycling clutch comprising rotatable input and output elements,cooperating drive engagement means on said elements respectively, one ofwhich is pivotally mounted on its associated element and biased forengagement with the engagement means on the other element, a rotatabletiming element adapted to bedriven by said input element and arranged tocome into engagement with said pivotally mounted engagement means toeffect release of the clutch at intervals greater than a revolution ofsaid input element, and means for maintaining said engagement meansdisengaged for a sufficient length of time to permit rotation of theoutput element in reverse direction under the influence of a biasingmeans through greater than one revolution.

2. A reproduction machine as claimed in claim 1, in which the inputelement includes a plate fixedly mounted on a drive shaft, and furtherincluding a pawl pivoted to said plate and biased to a position in whichsaid pawl drivingly engages the output element.

3. A reproduction machine as claimed in claim 2, including a drivingelement for driving said timing element, said driving element beingfixed against rotation with respect to the input element and adapted toengage said pawl once in each N revolutions, and wherein the ratio ofthe diameters of the timing and driving elements is N:l.

4. A reproduction machine as claimed in claim 2, and further including aramp disposed so as to be contacted by said pawl when said clutch is tobe held disengaged.

5. A recycling clutch comprising rotatable input and output elements,cooperating drive engagement means on said elements respectively, one ofwhich is pivotally mounted on its associated element and biased forengagement with the engagement means on the other element, a rotatabletiming element adapted to be driven by said input element and arrangedto come into engagement with said pivotally mounted engagement means toeffect release of the clutch at intervals greater than a revolution ofsaid input element, and means for maintaining said engagement meansdisengaged for a sufficient length of time to permit rotation of theoutput element in reverse direction under the influence of a biasingmeans through greater than one revolution.

1. A reproduction machine having a document scanning system, and animproved means for operating the latter, said means comprising: arecycling clutch comprising rotatable input and output elements,cooperating drive engagement means on said elements respectively, one ofwhich is pivotally mounted on its associated element and biased forengagement with the engagement means on the other element, a rotatabletiming element adapted to be driven by said input element and arrangedto come into engagement with said pivotally mounted engagement means toeffect release of the clutch at intervals greater than a revolution ofsaid input element, and means for maintaining said engagement meansdisengaged for a sufficient length of time to permit rotation of theoutput element in reverse direction under the influence of a biasingmeans through greater than one revolution.
 2. A reproduction machine asclaimed in claim 1, in which the input element includes a plate fixedlymounted on a drive shaft, and further including a pawl pivoted to saidplate and biased to a position in which said pawl drivingly engages theoutput element.
 3. A reproduction machine as claimed in claim 2,including a driving element for driving said timing element, saiddriving element being fixed against rotation with respect to the inputelement and adapted to engage said pawl once in each N revolutions, andwherein the ratio of the diameters of the timing and driving elements isN:1.
 4. A reproduction machine as claimed in claim 2, and furtherincluding a ramp disposed so as to be contacted by said pawl when saidclutch is to be held disengaged.
 5. A recycling clutch comprisingrotatable input and output elements, cooperating drive engagement meanson said elements respectively, one of which is pivotally mounted on itsassociated element and biased for engagement with the engagement meanson the other element, a rotatable timing element adapted to be driven bysaid input element and arranged to come into engagement with saidpivotally mounted engagement means to effect release of the clutch atintervals greater than a revolution of said input element, and means formaintaining said engagement means disengaged for a sufficient length oftime to permit rotation of the output element in reverse direction underthe influence of a biasing means through greater than one revolution.